Add support for MySQL notifications (fixes #3818) (#3907)

As a new configuration parameter is added, configuration version is
bumped up from 14 to 15.

The MySQL target's behaviour is identical to the PostgreSQL: rows are
deleted from the MySQL table on delete-object events, and are
created/updated on create/over-write events.

vendor/github.com/go-sql-driver/mysql/rows.go

@@ -0,0 +1,112 @@
+// Go MySQL Driver - A MySQL-Driver for Go's database/sql package
+//
+// Copyright 2012 The Go-MySQL-Driver Authors. All rights reserved.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package mysql
+
+import (
+	"database/sql/driver"
+	"io"
+)
+
+type mysqlField struct {
+	tableName string
+	name      string
+	flags     fieldFlag
+	fieldType byte
+	decimals  byte
+}
+
+type mysqlRows struct {
+	mc      *mysqlConn
+	columns []mysqlField
+}
+
+type binaryRows struct {
+	mysqlRows
+}
+
+type textRows struct {
+	mysqlRows
+}
+
+type emptyRows struct{}
+
+func (rows *mysqlRows) Columns() []string {
+	columns := make([]string, len(rows.columns))
+	if rows.mc != nil && rows.mc.cfg.ColumnsWithAlias {
+		for i := range columns {
+			if tableName := rows.columns[i].tableName; len(tableName) > 0 {
+				columns[i] = tableName + "." + rows.columns[i].name
+			} else {
+				columns[i] = rows.columns[i].name
+			}
+		}
+	} else {
+		for i := range columns {
+			columns[i] = rows.columns[i].name
+		}
+	}
+	return columns
+}
+
+func (rows *mysqlRows) Close() error {
+	mc := rows.mc
+	if mc == nil {
+		return nil
+	}
+	if mc.netConn == nil {
+		return ErrInvalidConn
+	}
+
+	// Remove unread packets from stream
+	err := mc.readUntilEOF()
+	if err == nil {
+		if err = mc.discardResults(); err != nil {
+			return err
+		}
+	}
+
+	rows.mc = nil
+	return err
+}
+
+func (rows *binaryRows) Next(dest []driver.Value) error {
+	if mc := rows.mc; mc != nil {
+		if mc.netConn == nil {
+			return ErrInvalidConn
+		}
+
+		// Fetch next row from stream
+		return rows.readRow(dest)
+	}
+	return io.EOF
+}
+
+func (rows *textRows) Next(dest []driver.Value) error {
+	if mc := rows.mc; mc != nil {
+		if mc.netConn == nil {
+			return ErrInvalidConn
+		}
+
+		// Fetch next row from stream
+		return rows.readRow(dest)
+	}
+	return io.EOF
+}
+
+func (rows emptyRows) Columns() []string {
+	return nil
+}
+
+func (rows emptyRows) Close() error {
+	return nil
+}
+
+func (rows emptyRows) Next(dest []driver.Value) error {
+	return io.EOF
+}